Methods of making thin reinforced tubular diaphragms and in diaphragms made according to these methods



P 1955 P. PLURIEN ETAL 3,270,414

METHODS OF MAKING THIN REINFORCED TUBULAR DIAPHRAGMS AND IN DIAPHRAGMS MADE ACCORDING TO THESE METHODS Filed March 28, 1961 2 Sheets-Sheet 1 S pt. 5. 1966 P. PLURIEN ETAL gg g DIAPHRAGMS MADE ACCORDING To THESE METHODS METHODS OF MAKING THIN REINFORCED TUBULAR DIAPHRAG 2 Sheets-Sheet z 0111'!!! II I I Filed March 28. 1961 United States Patent 3,270,414 METHODS OF MAKING THIN REINFORCED TUB- ULAR DIAPHRAGMS AND IN DIAPHRAGMS MADE ACCORDING TO THESE METHODS Pierre Plurien, Paris, Maurice Quenault Palaiseau, and Roger Rigot, Paris, France, assignors to Commissariat a lEnergie Atomique, Paris, France, an organization of France Filed Mar. 28, 1961, Ser. No. 98,917 Claims priority, application France, Mar. 30, 1960,

822,893 1 Claim. (Cl. 29527) In the prior US. patent application Serial No. 732,591, filed May 2, 1958, by Frances Boulet, Pierre Plurien, Maurice Quena-ult and Rogert Rigot, for Methods of Making Thin Reinforced Diaphragms and in Diaphragms Made According to These Methods, there is described a method of making thin diaphragms which comprises starting from a thin sheet of a metal a that is oxidizable to form a layer of oxide adhering strongly thereto, shaping said sheet so as to form stiffening ribs on one face thereof while leaving the other face smooth, and subjecting this smooth face to an oxidizing treatment, preferably an anodic one, until this treatment has transformed into oxide of the metal the whole thickness of the portion of the sheet located between the ribs while leaving the metal of the ribs unoxidized.

The articles thus obtained may be used in particular as microporous barriers for the separation of isotopes by gaseous diffusion.

The object of the present invention is to provide a process of manufacturing articles which are better adapted to meet the requirements of practice than those made up to this time.

The invention consists chieily in giving said articles a tubular shape before subjecting them to the oxidizing treatment, and preferably before the stiffening ribs have been formed.

The cross-section of the tubes made according to this invention may be of any shape whatever, for instance circular, polygonal (in the form of a hexagon, or an octogon or of a square for instance) elliptic or the like.

The ribs form on the surface of the tubular article a network the meshes of which (of square, round, or polygonal shape) limit flat recesses having a very thin bottom.

Preferably, the end portions of the tubes are left untreated to permit an easy fixation thereon of suitable end elements. A-dvantageously also, longitudinal and/or transverse bands of the tubes are left untreated so as thus to reinforce said tubes.

The metal or alloy of which the tubular elements are made may be any metal or alloy capable of being oxidized in an electrolyte to form a layer of oxide adhering strongly to the surface thereof.

Such substances are for instance the following metals: aluminum, magnesium, chromium, niobium, tantalum, titanium, vanadium, zirconium and hafnium and the alloys of these metals, for instance an alloy of aluminum and magnesium.

The thickness of the starting material depends upon the size and shape of the recesses to be formed therein. Generally, it ranges from 60 to 300 microns, preferably from 80 to 250 microns.

The shapes and dimensions of the recesses and also the thickness of their bottoms may vary according to the use for which the tubular elements are provided.

If these elements are to constitute fluid diffusion barriers, the maximum dimensions of the recess bottoms (i.e. their diameter if they are circular) should range from 150 to 1000 microns and preferably from 150 to 500 microns. The width of the ribs should range from 150 to 1000 micron-s and preferably from to 500 microns. The height of these ribs (in a direction perpendicular to the bottoms) may range from 50 to 250 microns and possibly more. As for the thickness of the bottoms of the recesses, that is to say the thickness of the metal or alloy transformed into oxide, it may range from 15 to 50 microns, and preferably from 15 to 40 microns.

The mechanical shaping of the starting metal may be performed either before or after the elements are given a tubular shape.

In the first case, a metal sheet is provided with the desired recesses and ribs, for instance by stamping or by rolling between a smooth cylinder and an engraved cylinder, after which the sheet is rolled up to form a tube, the edges of the sheet being welded together, before subjecting the smooth face to the oxidizing treatment. The edges of the sheet must be left unrecessed over a width sulficient to permit a good welding. This width is for instance twice that of the Weld.

In the second case, which is the preferred one, a thinwalled tube is first formed in a suitable manner, for instance by extrusion and drawing of the blank thus obtained or by rolling up a rectangular sheet the edges of which are then welded together. The ribs and recesses are then formed on one of the faces of the tube, preferably the outer face. The face of the tube which is not provided with ribs and recesses is then subjected to an oxidizing treatment, preferably an electrolytic one, the tube acting as an anode.

Preferred embodiments of the present invention will be hereinafter described with reference to the appended drawings given merely by way of example and in which:

FIG. 1 is a perspective view on an enlarged scale of a portion of a tubular barrier made according to the invention,

FIG. 2 shows a portion of said barrier in axial section on a still further enlarged scale, the true proportions having been preserved between the different dimensions,

FIGS. 3 and 4 diagrammatically show, respectively in side view and in section on the line -IVIV of FIG. 3, the shaping of a tubular element according to the invention.

FIGS. 5, 6 and 7 diagrammatically illustrate three other methods of shaping a tubular element.

FIG. 8 is a diagrammatical view illustrating the anodic oxidizing of a tubular element according to the invention.

In the drawings, reference numeral 1 designates the thin-Walled tube; 2 are the recesses provided in one face of said tube and 3 the ribs which form separations bet-ween these recesses. The recesses are formed by the teeth 4 of at least one tool.

FIGS. 3 to 7 illustrate the methods for forming the ribs and recesses on the external face of a tube 1.

This tube, the inner face of which is smooth, is engaged on a mandrel 5.

In the case of FIGS. 3 to 5 the mandrel is in the form of a prism having a hexagonal cross-section.

In the modification illustrated by FIGS. 3 and 4 the recesses are formed by two toothed wheels 6 acting upon two opposed faces of the tube and turning about axes perpendicular to the axis of the tube, the toothed wheel axes being kept at a suitable adjustable distance from each other, these axes being movable as a whole with respect to the mandrel which is supposed to remain stationary.

In the modification of FIG. 5 the two tools 7 are strongly applied against two opposed faces of tube 1 with a pressure which may range for instance from 5 to 15 tons per square centimeter.

The use of a prismatic mandrel having preferably an even number of sides (6, 8, 11 and so on) permits of forming the recesses very quickly over an important area.

In order to avoid the formation of brittle zones at the edges of the tube it is advantageous to give it subsequently the shape of a cylinder of revolution which is obtained by applying inside the tube a high fluid pressure or by passing this tube over a core having a suitable gradual section.

In the case of FIGS. 6 and 7, the mandrel is in a form of a cylinder of revolution.

In the modification of FIG. 6, two tools 8 having curvilinear working faces are strongly applied in the direction of the arrows, the teeth of said tools being of a shape calculated to permit an easy withdrawal of said tool after the operation.

In the modification of FIG. 7 the shaping of tube 1 is obtained by means of two rolling cylindrical toothed elements 9 turning about respective axes parallel to the axis of the tube, each of these elements 9 having in cross-section the shape of a circular sector. In the example illustrated by FIG. 7 there are two tool elements 9 disposed symmetrically with respect to the axis of tube 1 and the arc limiting each of the sectors has a length equal to one-half of the circumference of the cross-section of the tube. A rotation of tool 9 in the direction of the arrows therefore suffices to form the desired recesses over the whole area of the external face of the tube.

FIG. 8 illustrates the anodic oxidizing of a tube 1 provided with recesses 2 and the ribs 3. For this purpose, the ends of tube 1 are connected in liquid-tight fashion to a tank containing the electrolytic bath 11. A conductor rod 10 is placed in the tube, and tube 1 and rod 10 are electrically connected to the positive and the negative terminals, respectively, of a direct current source. Preferably, the electrolyte is made to circulate in the tube during electrolysis by means of a pump so as to improve the evacuation of heat. The curve giving the intensity of the current flowing through the electrolyte as a function of time may be recorded so that it is easy to determine when the bottoms of the recesses are wholly oxidized without the grid formed by ribs 3 being oxidized. This is indicated by a sudden rise of the current flow. This curve also perm-its of calculating by integration the amount of current that is necessary, which amount is constant for a given area and a given thickness of the barrier.

The following example having merely an indicative and non-limitative character, relates to the preparation of a barrier for the diffusion of gaseous uranium hexafluoride.

The starting element is a cylindrical tube made of an alloy of aluminum and magnesium containing 3% of magnesium obtained by extrusion without welding and having a diameter of mm, a length of 500 mm. and a Wall thickness of 0.1 mm.

This tube is fixed on a prismatic mandrel having an octagonal cross-section and the external surface of the tube is recessed by means of two toothed wheels having a diameter of 15 mm. and a thickness of 6 mm., two areas having a length of mm. being left without recesses at each end of the tube.

7 Each of the tools has, engraved in its periphery, two sets of lines at right angle to each other, these hollow lines having a width of 0.3 mm. and being at a distance of 0.8 mm. from each other (distance between the middle points of two consecutive lines). There is thus formed, on the external face of the tube, a grid made of ribs surrounding recesses in the form of squares, the sides of which are 0.5 mm. long, the height of said grid being 0.11 mm, the thickness of the recessed bottoms being 0.04 mm. so that the total thickness of the tube wall has passed from 0.10 to 0.15 mm. (see FIG. 2

After this operation, the tube is given a circular cylindrical shape by subjecting it to an inner pressure of for instance 2 or 3 kgs. per square centimeter.

I The inner face of the tube is then oxidized by an'elec- 4- trolytic method, as above described with reference to FIG. 8. Y

The electrolyte is an aqueous solution of oxalic acid at 7% kept at a temperature of 30 C. Cathode 9 is a rod of molybdenum.

The potential difference across the terminals of the direct current source is 36 volts and the current intensity is 1.2 amperes per square decimeter of the inner surface of the tube.

In order to oxidize the desired thickness (0.04 mm), the total amount of current is about 2.9 amperes/hour.

The tube thus obtained has an excellent optical transparency of the recess bottoms and its external metallic grill constitutes a reinforcement which is both strong (capable of withstanding a pressure of 4 kgs. per square centimeter applied on the inner wall of the tube) and flexible (thus avoiding risks of cracking of the tube when it is bent).

In order to adapt its permeability to the values required for diffusion barriers the impervious superficial layer of alumina forming the bottoms of the recesses is removed by attacking it in any suitable bath, for instance a mixture of phosphoric acid and ammonium fluoride. To reinforce the tubular barrier thus formed and in particular to avoid breaking thereof when it is handled, it is advantageously placed in a metallic case, corrugated and perforated so as to be in contact with the external grid of the tube only along the generatrices thereof.

In a general manner, while we have, in the above description, disclosed what we deem to be practical and eflicient embodiments of our invention, it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claim.

What we claim is:

The method of making a thin-walled tubular diaphragm which comprises forming a thin-walled tube of a metal which is oxidizable so as to form thereon a strongly adhering oxide layer, mechanically forming stiffening projecting ribs on the outer face of the wall of said tube While leaving the inner face smooth, placing a conductor rod in said tube, said rod being electrically insulated from said tube, circulating an electrolyte through said tube and connecting said rod and said tube to the respective terminals of a direct current source so as to exert an electrolytic oxidizing treatment on the inner surface of said tube, said treatment being pursued until the whole thickness of the portions of said tube extending between these ribs is oxidized without the metal of these ribs being oxidized.

References Cited by the Examiner UNITED STATES PATENTS 1,195,830 8/1916 McWane 138172 1,807,904 6/1931 Finley 138172 2,337,490 12/1943 Penner 29157.3 2,431,863 12/ 1947 Clifford.

2,687,565 8/1954 Schaefer et al. 29527 2,835,961 5/1958 Neel et al. 291573 2,912,751 11/ 1958 Turnbull 29527 3,089,235 5/1963 Boulet et al 29527 CHARLIE T. MOON, Primary Examiner.

WH'ITMORE A. WILTZ, Examiner.

E. H. MARTIN, J. C. HOLMAN, P. M. COHEN,

Assistant Examiners. 

